CN107915252B - Preparation method of nano titanium dioxide powder - Google Patents
Preparation method of nano titanium dioxide powder Download PDFInfo
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- CN107915252B CN107915252B CN201610879701.6A CN201610879701A CN107915252B CN 107915252 B CN107915252 B CN 107915252B CN 201610879701 A CN201610879701 A CN 201610879701A CN 107915252 B CN107915252 B CN 107915252B
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- 239000000843 powder Substances 0.000 title claims abstract description 144
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- 238000002360 preparation method Methods 0.000 title claims abstract description 24
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Classifications
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
- C01G23/00—Compounds of titanium
- C01G23/04—Oxides; Hydroxides
- C01G23/047—Titanium dioxide
- C01G23/053—Producing by wet processes, e.g. hydrolysing titanium salts
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
- B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
- B01J21/063—Titanium; Oxides or hydroxides thereof
-
- B01J35/39—
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y40/00—Manufacture or treatment of nanostructures
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/30—Three-dimensional structures
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
- C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/60—Particles characterised by their size
- C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
Abstract
The invention provides a preparation method of nano titanium dioxide powder, which comprises the following steps: dropwise adding titanium alkoxide into the acidic solution to perform hydrolysis reaction, and maintaining stirring until no precipitate is formed in the reaction system; the reaction system is shaded, sealed and kept stand until the reaction system is layered, and the lower layer liquid is completely transparent or blue phase transparent, or the reaction system becomes completely transparent or blue phase transparent liquid; taking transparent liquid in the reaction system, shading, sealing and standing for more than 10 days to obtain titanium dioxide sol; freeze-drying the titanium dioxide sol, controlling the freezing temperature of the freeze-drying to be-80 ℃ to-60 ℃ so that the burning loss of the nano titanium dioxide powder is 10-20%; wherein the titanium alkoxide satisfies the general formula Ti (OR)4R is C2-C4 alkyl; the ratio of titanium alkoxide to acidic solution is 0.05-2 mol: 1L of the compound. The nano titanium dioxide powder prepared by the preparation method provided by the invention has excellent dispersibility and photocatalytic activity.
Description
Technical Field
The invention relates to a preparation method of nano titanium dioxide powder, belonging to the technical field of nano materials.
Background
The nanometer titanium dioxide material is a functional nanometer material which develops rapidly in recent years, and has multiple characteristics of excellent photocatalytic activity, chemical stability, thermal stability, super-hydrophilicity, non-migration, nontoxicity and the like besides the specific surface effect, small-size effect, quantum effect and macroscopic quantum tunneling effect of the nanometer material, so that the nanometer titanium dioxide material can be used as a functional material such as an ultraviolet resistant material, a photocatalytic catalyst material and the like, and can be widely applied to products such as textiles, coatings, printing ink, sun cream, food packaging materials, paper making, lithium batteries, self-cleaning glass/substrates and the like. In the application of the nano titanium dioxide material as a raw material, according to the requirements of products and processes, the nano titanium dioxide powder generally needs to be subjected to subsequent processing and disposal, for example, compounding with other raw materials in the process, surface deposition of composite materials and the like, most of the operations need to be carried out in a dispersion solvent system (such as water or aqueous solvent), and the dispersion solvent is needed to avoid agglomeration of powder particles in each link from production, transportation to application of the nano titanium dioxide material. The good dispersibility of the nano titanium dioxide powder is the most basic requirement for meeting a plurality of application effects. However, the nano titanium dioxide powder is easy to agglomerate due to the properties of fine particles, large specific surface area, high surface energy, serious insufficient coordination and the like, so that the problems of difficult uniform dispersion, low dispersion concentration, low use efficiency, high application cost (including the cost of links such as storage, transportation and the like) and the like are solved no matter in the storage and transportation or application links, and the problems are the core problems to be faced and solved in the research and production of the nano titanium dioxide powder.
Aiming at the extremely easy agglomeration of the nano titanium dioxide powder, different solutions are proposed and applied, for example, the nano titanium dioxide powder is subjected to subsequent dispersion treatment (for example, a dispersing agent is introduced), and the dispersion characteristics of the powder are improved in a mode of reducing the surface energy of powder particles in a final product, adjusting the surface charge property of the powder particles and the like; it is also common to modify the surface of the titania colloidal particles in the sol system, especially to add a specific solvent (such as ethanol, propanol, and isopropanol), a dispersant/surfactant (such as polyethylene glycol 6000, sodium dodecyl sulfate, and a silane coupling agent), a chelating agent/complexing agent (such as acetylacetone), and rare metals to the titanium alkoxide hydrolysis system during the preparation of the titania sol using titanium alkoxide as a precursor, so as to coat a layer of organic or inorganic substances on the surface of the titania colloidal particles, and then to perform drying treatment such as high-temperature calcination, and obtain the titania powder with nano-scale dispersion dimensions. The technology for preparing the nano titanium dioxide powder by using the alcoholysis method is also used in the industry, and titanium salt is added into organic alcohol, and after alcoholysis is carried out under the condition of controlling a specific temperature, the titanium dioxide powder which can be dispersed in water in a nano scale can be obtained through solid-liquid separation, alcohol washing, drying and other treatments.
The nano titanium dioxide powder is prepared by dispersion treatment, or modification of the surface of titanium dioxide colloidal particles and alcoholysis, and the preparation process is complex and generally suffers from loss of application characteristics of products. Test results prove that no matter the nano titanium dioxide powder obtained through dispersion treatment or the nano powder material and other products prepared by taking the titanium dioxide sol obtained through modification treatment as a raw material, although the dispersion performance can meet the requirements, the application characteristics such as the photocatalytic activity of the nano titanium dioxide material are greatly reduced, and treating agents (including dispersing agents/surfactants, chelating agents/complexing agents, transition metals and the like) introduced in the sol modification and powder dispersion treatment process also lose the non-toxic characteristics of the nano titanium dioxide material, are difficult to remove in the subsequent processing process and even possibly bring secondary pollution to the final product; although the nano titanium dioxide powder prepared by the alcoholysis method meets the requirement of dispersion degree, the detection also finds that the particle size distribution is wide, the crystallization degree is low, the content of organic impurities is high and the like, and the defects are difficult to overcome while the photocatalysis efficiency is low.
Disclosure of Invention
The technical problem to be solved by the invention is to provide nano titanium dioxide powder and a preparation method thereof, which comprises the combination of process control for preparing titanium dioxide sol and freeze drying treatment for the sol, and the prepared nano titanium dioxide powder has excellent dispersibility and outstanding photocatalytic activity.
The invention provides a preparation method of nano titanium dioxide powder, which comprises the following steps:
dropwise adding titanium alkoxide into the acidic solution to perform hydrolysis reaction, and maintaining stirring until no precipitate is formed in the reaction system;
the reaction system is shaded, sealed and kept stand until the reaction system is layered, and the lower layer liquid is completely transparent or blue phase transparent, or the reaction system becomes completely transparent or blue phase transparent liquid;
taking transparent liquid in the reaction system, shading, sealing and standing for more than 10 days to obtain titanium dioxide sol;
freeze-drying the obtained titanium dioxide sol, controlling the freezing temperature of the freeze-drying to be-80 ℃ to-60 ℃, and enabling the burning loss of the obtained nano titanium dioxide powder to be 10-20%;
wherein, titaniumThe alkoxide satisfies the general formula Ti (OR)4R is C2-C4 alkyl; the ratio of the titanium alkoxide to the acidic solution is 0.05-2 mol: 1L of the compound.
The inventor researches and discovers that the processes of preparing high-quality sol raw materials and preparing powder by using the sol are two essential links for obtaining the nano titanium dioxide powder with excellent application performance and dispersibility, and besides the nano-scale dispersion effect, one of the important indexes of the powder is as follows: the excellence of the photocatalytic activity depends on whether the titanium dioxide sol raw material sent to the drying treatment process has higher photocatalytic activity and whether the photocatalytic activity of the sol can be maintained and improved in the process from drying to powder, namely, the photocatalytic activity of the nano titanium dioxide powder is obtained by controlling and matching the two processes.
The titanium alkoxide (also referred to as titanate) used in the preparation of the titania sol of the present invention may be ethyl, propyl, isopropyl, n-butyl, etc., and the commonly used titanium alkoxides include ethyl titanate (tetraethyl titanate), isopropyl titanate (tetraisopropyl titanate), tetrabutyl titanate (n-butyl titanate), etc.
In the course of dropping the titanium alkoxide into the acidic solution, in order to promote the hydrolysis of the titanium alkoxide to occur, it is a common practice to slowly drop the titanium alkoxide into the acidic solution (e.g., at a dropping rate of 1mL/min or less) and vigorously stir the acidic solution during this process. It can be understood that the hydrolysis efficiency of the titanium alkoxide can be improved by controlling the dropping speed of the titanium alkoxide and the stirring speed of the system.
The inventors have found that it is advantageous to control the hydrolysis reaction of the titanium alkoxide at a relatively low temperature, i.e., at or below room temperature, and in embodiments, the temperature of the acidic solution may be maintained at 0 to 20 ℃.
The dropwise addition of the titanium alkoxide is first completed under vigorous stirring, and then the rapid stirring can be adjusted and maintained for a certain time until no precipitate is formed in the reaction system. During the actual preparation, rapid stirring is generally maintained for 2 to 15 days.
When no precipitate is in the reaction system, the reaction system is shielded from light, sealed and kept standing, the hydrolysis reaction is continued until the reaction system becomes transparent and uniform liquid, obvious layering of the reaction system can be observed, the lower layer of the liquid is completely transparent or blue-phase transparent (the characteristic of the nano-scale dispersed titanium dioxide sol in the direct light), or no layering exists, but the reaction system becomes completely transparent or blue-phase transparent liquid, namely the hydrolysis reaction is considered to be completed, and the stage generally needs 10 to 30 days.
In the method, the hydrolysis reaction is completed in the acid solution, and the pH value of the acid solution is 1.8-3.
The acidic solution used in the present invention includes an organic acid solution and an inorganic acid solution, and specifically, may be an acidic aqueous solution obtained by mixing an inorganic acid or an organic acid with deionized water. The inorganic acid solution includes a nitric acid solution, a hydrochloric acid solution, an acetic acid solution, and the like, and may be, for example, a solution obtained by mixing nitric acid, hydrochloric acid, or acetic acid with deionized water.
After the hydrolysis reaction is finished, the transparent liquid taken from the reaction system can be a lower layer liquid which is completely transparent or blue-phase transparent when the reaction system is layered, or can be a completely transparent or blue-phase transparent liquid after the reaction, and the shading closed standing process at the stage is also called aging. The inventor researches and discovers that the performance of the titanium dioxide sol, particularly the photocatalytic activity is continuously improved along with the prolonging of the aging time, and the aging completion can be judged by monitoring the photocatalytic activity change condition of the sol in the aging process and ensuring that the photocatalytic degradation rate of methylene blue reaches 80% or higher. In the practical implementation process, the aging time needs more than 10 days, and the aging process can be completed. After the aging time exceeds 180 days, the photocatalytic degradation rate of the titanium dioxide sol still continues to increase but the change is not obvious, so the aging time is usually controlled to be 10 to 180 days. In the industrial production process, in order to take the performance and the production efficiency of the titanium dioxide sol into consideration, the aging time is usually 35 to 180 days, for example 35 to 140 days, and the titanium dioxide sol with better performance can be obtained.
The light-shielding closed standing is usually carried out by placing the reaction system in a closed reaction space, for example, in a closed and light-shielding reaction vessel (an enamel vessel, a polytetrafluoroethylene vessel, or the like which does not affect the reaction product, and standing at room temperature or at a temperature not more than 30 ℃).
The invention takes titanium alkoxide as a precursor, and obtains the titanium dioxide sol by controlling and adjusting the hydrolysis and aging processes of the titanium alkoxide in an acid solution. The research of the inventor finds that the titanium dioxide sol prepared by the method has smaller average dispersed particle size of titanium dioxide colloidal particles and narrower dispersed particle size distribution range, and then the nano titanium dioxide powder obtained by the freeze drying has excellent dispersibility, and the photocatalytic activity of the nano titanium dioxide sol raw material can be maintained, particularly the photocatalytic activity is excellent.
In the freeze drying process, the titanium dioxide sol is firstly frozen into a solid state, and then organic components, water and part of acidic medium in the titanium dioxide sol are directly sublimated into a gaseous state, so that the nano titanium dioxide powder is finally obtained. The invention ensures the performance of the dried powder by controlling the freezing temperature of the freeze drying to be-80 ℃ to-60 ℃. During sublimation in freeze drying, it is necessary to maintain a high vacuum level, and a relatively stable vacuum environment is more favorable for uniform drying of the powder. Especially when the treatment capacity is large, the relatively stable vacuum degree is controlled, the uniform and stable removal of water, solvent and acid medium is realized, and the burning loss of materials in different areas in the final drying cavity can reach the required burning loss. In a specific embodiment, the freeze drying is carried out, the vacuum degree in the sublimation process is controlled to be less than 15Pa (gauge pressure value), and the floating range is not more than +/-10%. Therefore, the freeze drying of the sol can be based on the control of the freezing temperature, and the vacuum degree in the cavity in the sublimation process is further controlled, so that the product characteristics are better controlled.
The inventor researches and discovers that when the burning loss of the nano titanium dioxide powder obtained by the freeze drying is 10-20%, the overall performance of the powder is better. The burning loss is too low or too high, which affects the performance of the powder, for example, if the burning loss of the powder is less than 10% due to too long freeze-drying time, the performance of the powder is unstable, and if the freeze-drying time is insufficient, the burning loss of the powder is more than 20%, the powder is difficult to store due to easy moisture absorption.
In actual operation, the specific time of the freeze-drying process can be properly adjusted within the above range according to the performance index of the freeze-drying apparatus, in addition to the freezing temperature and the pressure during sublimation. In the specific implementation mode of the invention, the freeze drying can be finished after about 30 to 60 hours, and the nano titanium dioxide powder with better overall performance is prepared.
The invention also provides nano titanium dioxide powder which is prepared by adopting the method.
Specifically, the nano titanium dioxide powder prepared by the preparation method provided by the invention has the grain size of less than 25nm and the dispersed grain size of less than 100nm in water.
The invention provides a preparation method of nano titanium dioxide powder, which is characterized in that the nano titanium dioxide powder prepared by controlling the hydrolysis and aging processes of titanium alkoxide and matching with a specific freeze drying process has the following characteristics:
(1) the grain size of the powder is less than 25nm, and the powder has an anatase crystal structure;
(2) the powder can be well dispersed in water by stirring according to conventional operation without special equipment when being added into water, and the nano titanium dioxide dispersion liquid with better stability can be obtained even if the powder is added according to the mass concentration of 50%. It is found by dispersion experiments that when the powder of the present invention is dispersed in water at a content of not more than 10 wt%, the obtained dispersion system can maintain good light transmittance and stability, and when the content is low, for example, less than 1%, the dispersion liquid is almost transparent liquid, and gradually becomes semitransparent milky white liquid with the increase of the content. The maximum dispersed particle size of titanium dioxide powder in the dispersion liquid is less than 100nm, and the powder cannot easily agglomerate;
(3) according to the test of national standard (GB/T23762-2009), the removal rate of the nano titanium dioxide powder to methylene blue is higher than 80% and even reaches more than 90% (which is directly shown in that after the methylene blue solution is irradiated by ultraviolet light for 2 hours, the solution is changed from dark blue to light blue or light purple, and even approaches to colorless and transparent).
The invention not only provides a preparation process of titanium dioxide sol, but also prepares titanium dioxide powder by a freeze drying technology, realizes effective drying of materials, and provides nano titanium dioxide powder with good dispersibility and controlled water absorption. The freeze drying technology is widely applied to the production field of medicines and fruits and vegetables, and aims to remove moisture as much as possible. The invention introduces the freeze drying technology when drying the titanium dioxide sol particles, and adjusts the drying parameters to obtain a powder product with a certain burning loss, thereby endowing the powder with nano-scale dispersion and low water absorption (difficult agglomeration). The inventor researches and discovers that if the freeze drying process and operation of the medicines or fruit and vegetable foods are directly introduced, after the drying is finished, the dried products coming out of different areas of the chamber can show very non-uniformity and have very different burning loss amounts, for example, the burning loss amount of the materials at the top of the chamber is very low, while the materials at the bottom of the chamber are still in a flowing state or a viscous liquid state; even if the powder reaches the drying standard, the powder has obvious yellowing in appearance, strong water absorption, rapid hydration and difficult use.
In conclusion, the nano titanium dioxide powder prepared by the invention has an anatase crystal structure and smaller grain size; the nano titanium dioxide powder has excellent dispersibility in water, and the obtained dispersion system has good light transmittance and stability, so that the nano titanium dioxide powder can be dispersed at a high concentration in a nanoscale level in the application process, and the nano titanium dioxide powder can be stably dispersed in water at a high concentration, so that the storage, transportation and application costs of the nano titanium dioxide powder are greatly reduced; the powder keeps the application characteristics of the nano titanium dioxide material, and particularly has outstanding photocatalytic activity.
Because the nano titanium dioxide powder prepared by the method has the characteristics, the modification treatment on the titanium dioxide sol is not needed, and the further dispersion treatment on the nano titanium dioxide powder is also not needed, so that the introduction of impurities is avoided, and the production and the application of related products of nano titanium dioxide materials are facilitated.
Drawings
FIG. 1 is an XRD pattern of a nano-titania powder prepared in example 1 of the present invention;
FIG. 2 is a distribution curve of the dispersed particle size of the nano-titania powder prepared in example 1 of the present invention in water.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are a part of the embodiments of the present invention, but not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the invention, the crystal forms of the titanium dioxide colloidal particles and the nano titanium dioxide powder are both determined by an X-ray diffractometer, and the grain size is automatically calculated and given by the X-ray diffractometer according to the Sheer formula; the dispersed particle size is measured by a Zeta potential and nanometer particle size analyzer (the particle size measuring range is 3-6000nm, and is the measuring range of the Zeta potential and nanometer particle size analyzer). Unless otherwise specified, the dispersed particle size in the present invention is calculated by a weighted average in terms of mass.
The photocatalytic degradation rate of the sol and the powder to methylene blue is determined according to the national standard purification test method for photocatalytic material aqueous solution systems (GB/T23762-2009), and the specific test method comprises the following steps:
preparing methylene blue solution with concentration of 10mg/L, measuring absorbance (ultraviolet-visible spectrophotometer, the same below), and recording as A0(ii) a Putting the newly prepared methylene blue solution into a reaction vessel, and weighing 0.1g of nano titanium dioxide powder in the reaction vessel for a powder sample; for the sol sample, the sampling amount is determined by taking 0.1g of nano titanium dioxide powder as a reference, and the sol sample is also placed in a reaction vessel; adjusting the height of the reaction container and ultraviolet lamp (wavelength of 254nm) to make the light intensity on the surface of the solution within the allowable range, then starting the magnetic stirrer, finally turning on the ultraviolet lamp, and the irradiation intensity at the bottom of the cup is 0.8mw/cm2The liquid level irradiation intensity is 1.3mw/cm2(irradiation of the entire UV lightAll processes are carried out in a dark box); after 2 hours of reaction, stirring and ultraviolet irradiation were stopped, the mixture was left to stand for 20 minutes, and the supernatant was collected and the absorbance was measured and recorded as At。
the calculation formula of the photocatalytic degradation rate η of the methylene blue is that η is (A)0-At)/A0the larger the value of the photocatalytic degradation rate η of the methylene blue is, the higher the photocatalytic activity of the titanium dioxide sol or the nano titanium dioxide powder is.
The burning loss of the nano titanium dioxide powder is calculated according to the mass reduction of a sample after the sample is burned at a certain temperature until the quality is constant, and the specific test method comprises the following steps:
weighing 1g (accurate to 0.0002g) of nano titanium dioxide powder sample, placing the sample in a ceramic crucible, covering the crucible cover with a little gap, and placing the ceramic crucible in a muffle furnace to burn (the temperature is 550-600 ℃) until the quality is unchanged.
The calculation formula of the burning loss W is as follows: w ═ m1-m2) M.times.100%, where m1And m2The mass sum of the porcelain crucible and the nano titanium dioxide powder sample before and after burning respectively, and m is the mass of the nano titanium dioxide powder sample. Taking the arithmetic mean value of the results of the parallel determination as the measurement result, and the absolute value of the results of the two parallel determinations is not more than 0.3 percent.
Examples 1 to 4
The preparation of the nano titanium dioxide powder comprises the following steps:
a. dropwise adding titanium alkoxide into a vigorously stirred nitric acid solution at the speed of 1mL/min, and controlling the temperature of a reaction system to be maintained at a hydrolysis temperature, wherein the nitric acid solution is prepared by mixing deionized water and nitric acid;
b. after the titanium alkoxide is dripped, continuously maintaining the temperature of the reaction system at the hydrolysis temperature and rapidly stirring for a certain time until no precipitate is formed in the reaction system;
c. placing the reaction system in an enamel reaction tank, sealing and ensuring shading standing, wherein in the process, the reaction system continuously keeps the hydrolysis temperature, and after a certain standing time and a certain standing time, the reaction system is layered and the lower layer is transparent or blue-phase transparent or the system is completely transparent or blue-phase transparent;
d. taking the transparent liquid of the system, sealing and standing for aging at a dark place, keeping the temperature at the aging temperature, and obtaining titanium dioxide sol after a certain aging time, wherein the crystal size and the dispersed particle size of the titanium dioxide colloidal particles and the test results of the photocatalytic degradation rate of the titanium dioxide sol to methylene blue are shown in table 1;
e. placing the obtained titanium dioxide sol in a freeze drying device (model is TF-SFD-200, the same below), adjusting freezing temperature and vacuum degree, obtaining nano titanium dioxide powder after certain freeze drying time, and testing the burning loss of the nano titanium dioxide powder.
In the preparation process of the nano titanium dioxide powder, the type and mass of titanium alkoxide, the volume and pH value of a nitric acid solution, the hydrolysis temperature in the steps a to c, the rapid stirring time in the step b, the standing time in the step c, the aging temperature and the aging time in the step d, the content of titanium dioxide in the obtained titanium dioxide sol, and the freezing temperature, the drying vacuum degree, the freeze-drying time and the burning loss in the step e are shown in table 1.
TABLE 1 TABLE of Process parameters and test results for examples 1-4 and comparative example 1
Layering the reaction systems of the embodiment 1 and the embodiment 3, taking the transparent liquid at the lower layer for standing and aging, wherein the liquid at the lower layer is completely transparent or transparent in a blue phase; the reaction systems of the examples 2 and 4 are completely transparent or blue phase transparent liquid, so the liquid is directly used for standing and aging in the next step.
Fig. 1 is an XRD pattern of the nano titanium dioxide powder prepared in example 1, and XRD patterns of the nano titanium dioxide powders prepared in examples 2-4 are similar to those of fig. 1, and all show very obvious diffraction peaks at 25.4 ° 2 θ, which confirms that all crystal forms of the nano titanium dioxide powders prepared in examples 1-4 are anatase crystal forms, and the specific grain sizes are shown in table 1.
The nano titanium dioxide powder prepared in the examples 1 to 4 is added into deionized water, and a basically uniform nano titanium dioxide dispersion liquid (the mass concentration of the nano titanium dioxide powder in the dispersion liquid is shown in table 1) is quickly obtained by adopting a common stirring mode, the dispersion liquid obtained in the example 3 is semitransparent bluish white with certain light transmittance by visual inspection, and the dispersion liquids obtained in the examples 1, 2 and 4 have a transparent blue phase and good light transmittance.
FIG. 2 is a distribution curve of the dispersed particle size of the powder in the nano-titania dispersion obtained in example 1, and the distribution curves of the dispersed particle size of the nano-titania powders obtained in examples 2 to 4 in water are similar to those in FIG. 2, and both of them are typical normal distribution and have a narrow distribution range of the dispersed particle size, and specific values are shown in Table 1.
The nano titanium dioxide dispersion liquid obtained in the examples 1 to 4 is kept stand for 90 days, no obvious layering and precipitation are observed, and the re-detection shows that the dispersion particle size distribution of the nano titanium dioxide dispersion liquid is basically kept unchanged, which indicates that the nano titanium dioxide powder does not obviously agglomerate in water, and the performance of the nano titanium dioxide dispersion liquid is very stable.
The photocatalytic degradation rate of methylene blue was determined by using the nano titanium dioxide powder photocatalytic degradation methylene blue solution prepared in examples 1-4, and the results are shown in table 1, which are all higher than 80%, even more than 90%. It can be observed by visual inspection that the methylene blue solution is originally dark blue transparent liquid, and after the nano titanium dioxide powder is added and irradiated by ultraviolet light for 2 hours, the methylene blue solution becomes light blue or light purple, and the methylene blue solution in examples 1, 2 and 4 is even nearly colorless and transparent, which shows that the nano titanium dioxide powder prepared in examples 1-4 has very high photocatalytic activity.
The nano titanium dioxide powder obtained by the preparation method in the embodiment 1-4 is in anatase crystal form, and the grain size is 4-25 nm; dispersing the nano titanium dioxide powder in water, and directly stirring the nano titanium dioxide powder by a conventional method to obtain a nano titanium dioxide dispersion liquid with good dispersibility and high stability, wherein the dispersion particle size distribution of the nano titanium dioxide dispersion liquid is in a typical normal distribution, the maximum dispersion particle size is less than 100nm, and the dispersion particle size distribution range is narrow; the nano titanium dioxide powder is adopted to carry out photocatalytic degradation on the methylene blue solution, when the solution is irradiated by ultraviolet light for 2 hours, the methylene blue solution is changed from dark blue to light blue or light purple, even is nearly colorless and transparent, and the photocatalytic degradation rate of the methylene blue is higher than 80 percent and even higher than 90 percent through test calculation. Therefore, the preparation method provided by the invention comprises the combination of the process control for preparing the titanium dioxide sol and the freeze drying treatment for the sol, not only can anatase type nano titanium dioxide powder with very small grain size be obtained, but also the powder has very excellent dispersing performance and photocatalytic activity.
Comparative example 1
In this comparative example, the preparation method of the nano titanium dioxide powder is substantially the same as that in example 2, except that the preparation process of the titanium dioxide sol is not subjected to standing aging in step d, but the transparent liquid obtained in step c is directly taken and placed in a freeze drying device for freeze drying, and the specific process conditions of freeze drying are the same as those of step e in example 2, which is specifically shown in table 1.
The titanium dioxide sol prepared in the comparative example 1 was tested to be in anatase crystal form, the grain size thereof was 5nm, and the photocatalytic degradation rate of methylene blue thereof was 16%.
The nano titanium dioxide powder prepared in comparative example 1, which was in the anatase crystal form and had a grain size of 5nm, was dispersed in water to obtain a nano titanium dioxide dispersion having a mass concentration of 6 wt%, and the dispersed grain size distribution data thereof was measured as shown in table 1.
The photocatalytic degradation rate of the nano titanium dioxide powder prepared in comparative example 1 on methylene blue was 31%. It can be observed by visual inspection that the methylene blue solution is initially a dark blue transparent liquid, and the methylene blue solution turns into light blue after the nano titanium dioxide powder is added and irradiated by ultraviolet light for 2 hours.
Therefore, the nano titanium dioxide powder obtained by the method of comparative example 1 had an anatase structure and a small grain size, and had good dispersibility, but had low photocatalytic activity.
Comparative example 2
In this comparative example, the titanium dioxide sol is prepared by adopting the technical scheme of example 4 in chinese patent 200710065655.7, specifically:
adding tetrapropyl titanate into distilled water, adding a small amount of acetylacetone and nitric acid at the same time, controlling the pH of a reactant to be 2, and stirring at the temperature of 70 ℃ for 7 hours under normal pressure to obtain titanium dioxide sol. Wherein the molar ratio of the tetrapropyl titanate, the water, the acetylacetone and the nitric acid is 1: 150: 0.7: 0.005.
According to tests, the titanium dioxide sol prepared in the comparative example 2 is in an anatase crystal form, the grain size of the titanium dioxide sol is 7nm, and the photocatalytic degradation rate of the titanium dioxide sol on methylene blue is 12%.
Placing the titanium dioxide sol in a freeze drying device (model: TF-SFD-200), wherein the freezing temperature is-65 ℃, the vacuum degree is stably controlled to be 3Pa (the up-down fluctuation does not exceed 0.3Pa), and after about 38 hours, obtaining the nano titanium dioxide powder, and testing that the burning loss is 19%.
According to tests, the nano titanium dioxide powder prepared in the comparative example 2 is in an anatase crystal form, the grain size is 7nm, and the nano titanium dioxide powder is dispersed in deionized water to obtain a nano titanium dioxide dispersion liquid with the mass concentration of 6 wt%, the dispersion grain size range is 7-40nm, and the average dispersion grain size is 16 nm.
The photocatalytic degradation rate of the nano titanium dioxide powder to methylene blue is 30%. It can be observed by visual inspection that the methylene blue solution is initially a dark blue transparent liquid, and the methylene blue solution turns into light blue after the nano titanium dioxide powder is added and irradiated by ultraviolet light for 2 hours.
Therefore, the titanium dioxide sol prepared by the conventional method has very low photocatalytic activity; the nano titanium dioxide powder obtained by specific freeze drying treatment has an anatase crystal form and a very small grain size, has excellent dispersing performance in water, and has the photocatalytic activity slightly improved compared with that of titanium dioxide sol, but far lower than that of the nano titanium dioxide powder prepared by the method.
Comparative example 3
The titania sol was prepared using the procedure of steps a-d in example 2.
The conventional drying treatment is carried out on the titanium dioxide sol, and the reference documents of Xuyuehua, Guguoban and the like, the preparation and characterization of high-activity nano titanium dioxide and the photocatalytic performance [ J ] functional materials, the journal of 2004 (35): 2764-2767 ", the drying process comprises the following specific steps: the titanium dioxide sol is placed for 1 day, dried in a drying oven at 65 ℃, ground in an agate mortar and then calcined in a muffle furnace at 350 ℃ (the transition temperature of the titanium dioxide from an amorphous state to an anatase phase) to obtain the nano titanium dioxide powder.
The above-mentioned nano titanium dioxide powder was subjected to a conventional modification treatment, and the surface modification of titanium dioxide powder was studied by the literature "zhangmaxi, rubens." study of chemical and adhesion, 2011, 33 (1): 21-23 ", the specific process is as follows: weighing 5.0g of titanium dioxide powder, placing the titanium dioxide powder in a drying oven, drying the titanium dioxide powder for 30min at the temperature of 100 ℃, weighing a silane coupling agent KH550 (gamma-aminopropyltriethoxysilane, New chemical Material Co., Ltd., Cheng & Shen, Conn. of chemical engineering Co., Ltd.) with corresponding mass, placing the weighed titanium dioxide powder into a beaker, adding 10mL of absolute ethyl alcohol, adding hydrochloric acid or sodium hydroxide to adjust the pH value to 7, adding a coupling agent solution into a dry three-neck flask containing the titanium dioxide powder, adding 40mL of absolute ethyl alcohol, refluxing and condensing, placing the flask in a water bath to heat, and stirring and reacting for 3 h. The system is white stable emulsion all the time in the reaction process, and the temperature of the system is stable at 80 ℃. And after the reaction is finished, cooling the system to room temperature, placing the product in a beaker, and drying the product in a drying oven at 100 ℃ for 24 hours to obtain the modified nano titanium dioxide powder.
Tests show that the grain size of the nano titanium dioxide powder obtained after the modification treatment is 19 nm. The titanium dioxide powder is added into deionized water, ultrasonic dispersion is carried out in the adding process to obtain nano titanium dioxide dispersion liquid with the concentration of 6 wt%, the dispersion liquid is visually inspected to be milky turbid, and the average dispersed particle size of the titanium dioxide powder is 640 nm.
In the comparative example, the nano titanium dioxide powder is prepared by calcining the titanium dioxide sol at high temperature, but the powder is seriously agglomerated in the high-temperature calcining process, even if the powder is subjected to surface modification treatment and is dispersed by ultrasonic, the submicron-level dispersion of the powder in water can be only completed, and the stability and the uniformity of a dispersion liquid are poor.
Therefore, the nanometer titanium dioxide powder prepared by the conventional drying and modification treatment of the titanium dioxide sol prepared by the method has extremely poor dispersibility in water, and is very unfavorable for transportation, storage and application of the nanometer titanium dioxide powder.
Comparative example 4
In this comparative example, the preparation method of the nano titanium dioxide powder is basically the same as the technical scheme of the embodiment 4, except that the burning loss of the finally obtained nano titanium dioxide powder is 5-6% after about 47 hours of freeze drying.
According to tests, the nano titanium dioxide powder prepared in the comparative example 4 is in an anatase crystal form, the grain size is 5nm, and the nano titanium dioxide powder is dispersed in deionized water to obtain a nano titanium dioxide dispersion liquid with the mass concentration of 6 wt%, the dispersion grain size range is 10-830nm, and the average dispersion grain size is 410 nm. And the photocatalytic degradation rate of the nano titanium dioxide powder to methylene blue is 63%.
Since the burning loss of the nano titanium dioxide powder in the comparative example is less than 10%, the dispersion performance and the photocatalytic activity of the powder are poor.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (7)
1. A preparation method of nano titanium dioxide powder is characterized by comprising the following steps:
dropwise adding titanium alkoxide into the acidic solution to perform hydrolysis reaction, and maintaining stirring for 2-15 days until no precipitate is formed in the reaction system;
the reaction system is shaded, sealed and kept stand until the reaction system is layered, and the lower layer liquid is completely transparent or blue phase transparent, or the reaction system becomes completely transparent or blue phase transparent liquid;
taking transparent liquid in the reaction system, shading, sealing and standing for more than 10 days to obtain titanium dioxide sol;
freeze-drying the titanium dioxide sol, controlling the freezing temperature of the freeze-drying to be-80-60 ℃, controlling the vacuum degree in the sublimation process to be less than 15Pa, and ensuring the floating range not to exceed +/-10 percent, so that the burning loss of the obtained nano titanium dioxide powder is 10-20 percent at the temperature of 550-600 ℃;
wherein the content of the first and second substances,
the titanium alkoxide satisfies the general formula Ti (OR)4R is C2-C4 alkyl;
the acid solution is an acid aqueous solution formed by mixing inorganic acid or organic acid with deionized water;
the ratio of the titanium alkoxide to the acidic solution is 0.05-2 mol: 1L of the compound.
2. The production method according to claim 1, wherein the temperature of the acidic solution is maintained at 0 to 20 ℃ during the dropwise addition of the titanium alkoxide to the acidic solution.
3. The method according to claim 1 or 2, wherein the acidic solution has a pH of 1.8 to 3.
4. The method according to claim 1, wherein the acidic solution is a nitric acid solution, a hydrochloric acid solution, or an acetic acid solution.
5. The method according to claim 3, wherein the acidic solution is a nitric acid solution, a hydrochloric acid solution, or an acetic acid solution.
6. The production method according to claim 1, wherein the titanium dioxide sol is obtained by allowing a transparent liquid in the reaction system to stand in a light-shielding, sealed and closed manner for 10 to 180 days.
7. The nano titanium dioxide powder obtained by the preparation method of any one of claims 1 to 6, wherein the crystal grain size of the nano titanium dioxide powder is less than 25nm, and the dispersed grain size in water is less than 100 nm.
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Effective date of registration: 20200805 Address after: Room 305, No. 11, Suzhou nanchengxi North District, No. 99, Suzhou nanchengxi area, Suzhou Industrial Park, Suzhou, Jiangsu Co-patentee after: Suzhou Baoshun Mei Technology Co.,Ltd. Patentee after: Qu Haifeng Address before: Room 305, No. 11, Suzhou nanchengxi North District, No. 99, Suzhou nanchengxi area, Suzhou Industrial Park, Suzhou, Jiangsu Patentee before: Qu Haifeng |